CA-1000 Class A Question

audiomaniac

Active Member
I just got a CA-1000 and it sounds very nice indeed. While I was waiting for it to arrive, I had been reading about the Class A ability of the amp, 15 watts I believe. After listening in normal mode for about an hour, I shut the amp off, waited about a minute, and then selected Class A before turning it back on. I do not hear any difference in sound and I turn the volume up to the exact same level as I was listening to before at the normal setting. Does this indicate that something is wrong? Is there a way to tell if Class A is working for sure? So far, all other functions seem fine. Thanks!
 
I just got a CA-1000 and it sounds very nice indeed. While I was waiting for it to arrive, I had been reading about the Class A ability of the amp, 15 watts I believe. After listening in normal mode for about an hour, I shut the amp off, waited about a minute, and then selected Class A before turning it back on. I do not hear any difference in sound and I turn the volume up to the exact same level as I was listening to before at the normal setting. Does this indicate that something is wrong? Is there a way to tell if Class A is working for sure? So far, all other functions seem fine. Thanks!

Class A is very subtile difference. The only difference is lower crossover distortion of the sine wave. That and the amplifier will run a lot hotter:D..Will take a real good ear to notice the difference sound wise.
 
Thanks for the response. I'm not a tech type, unfortunately, so I'm limited in my investigation abilities. I guess if it sounds good, it IS good!
 
I find that class a has a subtle difference in detail and ambience in my ca-800. It really isn't the type of difference that makes you say "wow". Listen critically to something that was well recorded in class ab then again in class a and see if you hear more detail or if the music "breathes" a bit more...again it tends to be a subtle difference and not very striking.
 
OK. I will say that I am really enjoying it in the "Normal" setting. I'm using a MM cartridge and the phono is excellent. Dead quiet. The amp was recapped except for the phono stage. Hard to believe it sounds this good for its age!

I find that class a has a subtle difference in detail and ambience in my ca-800. It really isn't the type of difference that makes you say "wow". Listen critically to something that was well recorded in class ab then again in class a and see if you hear more detail or if the music "breathes" a bit more...again it tends to be a subtle difference and not very striking.
 
I find that class a has a subtle difference in detail and ambience in my ca-800. It really isn't the type of difference that makes you say "wow". Listen critically to something that was well recorded in class ab then again in class a and see if you hear more detail or if the music "breathes" a bit more...again it tends to be a subtle difference and not very striking.
Agreed...I think it does sound better - I would add smoother and a little richer. But subtle is the word.
 
Initially when there was only Class A and Class B the difference was more pronounced, Now that we mostly have Class AB the difference is very subtle.

In Class A the output transistors are never switched 'off' so no 'crossover distortion' but lots of heat.

In class B the two output transistors were only switched "on" as the sine wave went positive or negative. This switching was not instantaneous so there was a short interval when there was no output, giving a flat spot at crossover, hence the name 'crossover distortion'.

Class AB got around this problem by not switching the output transistors completely 'off'. We see this as 'bias current' or 'bias voltage" and this has the outputs drawing a small current and so they switch instantaneously.
 
Initially when there was only Class A and Class B the difference was more pronounced, Now that we mostly have Class AB the difference is very subtle.

In Class A the output transistors are never switched 'off' so no 'crossover distortion' but lots of heat.

In class B the two output transistors were only switched "on" as the sine wave went positive or negative. This switching was not instantaneous so there was a short interval when there was no output, giving a flat spot at crossover, hence the name 'crossover distortion'.

Class AB got around this problem by not switching the output transistors completely 'off'. We see this as 'bias current' or 'bias voltage" and this has the outputs drawing a small current and so they switch instantaneously.

Great explanation...even if I don't completely understand what it all means; at least I have a clearer picture:yes:
 
Thanks for the info merrylander! Now it makes more sense. I can't really hear too much difference, if any, on my CA1000 between normal and Class A, however, the normal setting sounds very sweet. I read somewhere that if the switch gets fried, the amp will stay in Class A or somewhere in between Class A and normal. I've also read that you can make the switch fail by switching between the two settings with the amp powered in. That's what I wonder about mine, if the previous owner was careful not to do that. I can play it for hours and noticed last night it was pretty hot after running it for about 7 hours on the normal setting. I guess it's all subjective with me and maybe I'll have it looked at for peace of mind. But right now the Normal setting is fine with me! Glad to be part of the Yamaha owners group!:banana:


Initially when there was only Class A and Class B the difference was more pronounced, Now that we mostly have Class AB the difference is very subtle.

In Class A the output transistors are never switched 'off' so no 'crossover distortion' but lots of heat.

In class B the two output transistors were only switched "on" as the sine wave went positive or negative. This switching was not instantaneous so there was a short interval when there was no output, giving a flat spot at crossover, hence the name 'crossover distortion'.

Class AB got around this problem by not switching the output transistors completely 'off'. We see this as 'bias current' or 'bias voltage" and this has the outputs drawing a small current and so they switch instantaneously.
 
After listening in normal mode for about an hour, I shut the amp off, waited about a minute, and then selected Class A before turning it back on.

I have a 1983 A-1000 10 watts lass A, 120 wpc AB. I have moved it from A to AB without turning it off :scratch2: have I damaged anything?? Also the only time I can notice any difference is in Class A is at low volume 75 Db or so, my bass is more pronounced on my Klipsch Cornwall speakers. After 75 Db or so I can't hear any difference either mode. I usually don't bother with Class A as I listen to my music a bit louder and I don't like the extra heat. I have a fan mounted behind it and all my amps...
 
I have moved it from A to AB without turning it off have I damaged anything??

No.Auto class A you can switch back and forth without issues.
 
I've enjoyed my CA-1000 for years without using the Class A switch.
Except when used in party situations and at normal listening levels, I think the amp may have never left Class A mode, YMMV:)
 
Ideally it would be yes, but in practice, with the CA-1000 uses microswitches in the class A switch and these are notorious for issues. They not only change bias but also secondary transformer tappings.
Class A/AB switchable vintage amps should not, as a general rule be switched between classes when on. I have seen the results of CA-1000s taking out their output stages when one microswitch goes bad and the entire amp gets an unbalanced pair of rails.


No.Auto class A you can switch back and forth without issues.
 
Ideally it would be yes, but in practice, with the CA-1000 uses microswitches in the class A switch and these are notorious for issues. They not only change bias but also secondary transformer tappings.
Class A/AB switchable vintage amps should not, as a general rule be switched between classes when on. I have seen the results of CA-1000s taking out their output stages when one microswitch goes bad and the entire amp gets an unbalanced pair of rails.

I was refering to LAB3's A-1000
1983 A-1000 10 watts lass A, 120 wpc AB.

not the CA-1000 and I concur. I too have seen and replaced a few fried micro switches.

BTW The micro switches, on the CA-800/1000, don't switch the bias. The center slide switch does. The M-switches only switch the x-transformer taps.
 
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I'm not a fan of amps that switch the secondary rail voltages via switches or relays. Sadly, the Yamaha and Marantz amps with those 'features' I have seen cross my bench all too often and it is primarily due to the rail switching. Even Pioneers with their 'impedance switches' have more than their fair share of troubles. It would have been much more sensible to have a switch like the old octal style voltage selectors (on the back of gear) where the class of operation could be changed via hard wired jumper plugs with the power off- less contact resistance and/or opportunity for failures.

My Marantz PM95 uses a slide switch on the back and twin 10A relays for secondary taps along with optocoupler driven bias selection, and that was an improvement on the 'automatic' Class A on the PM94 which was prone to fail and cook itself.

The fact that the CA-1000 switch can engage one rail microswitch before the other if the toggle is moved slowly is enough to justify doing it off in my opinion.
 
I'm not a fan of amps that switch the secondary rail voltages via switches or relays. Sadly, the Yamaha and Marantz amps with those 'features' I have seen cross my bench all too often and it is primarily due to the rail switching. Even Pioneers with their 'impedance switches' have more than their fair share of troubles. It would have been much more sensible to have a switch like the old octal style voltage selectors (on the back of gear) where the class of operation could be changed via hard wired jumper plugs with the power off- less contact resistance and/or opportunity for failures.

My Marantz PM95 uses a slide switch on the back and twin 10A relays for secondary taps along with optocoupler driven bias selection, and that was an improvement on the 'automatic' Class A on the PM94 which was prone to fail and cook itself.

The fact that the CA-1000 switch can engage one rail microswitch before the other if the toggle is moved slowly is enough to justify doing it off in my opinion.

Again, I concur with the CA-1000 and CA-800.They are the only two Yamaha's that use omron microswitches,unless there are some european models that do as well. for rail switching. Auto-class A as in the M series amps ,switch the rails with power transistors.Therefore they can be switched on the fly without issues.
The CA-1010 and CA-2010 uses a relay to switch rails.
 
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